Light neutral mesons production in p-A collisions at $\sqrt{s} = 27.5$ GeV with the NA60 Experiment

Abstract

The NA60 experiment has studied low-mass muon pair production in proton-nucleus (p-A) collisions with a system of Be, Cu, In, W, Pb and U targets using a 400 GeV/$c$ proton beam at the CERN SPS. Thanks to the collected data sample of 180\,000 low mass muon pairs, the most precise measurement currently available was performed for the electromagnetic transition form factors of the $\eta$ and $\omega$ mesons. The $\rho$ line shape was quantitatively investigated, and its effective temperature measured for the first time in elementary collisions. The transverse momentum spectra for the $\omega$ and $\phi$ mesons have been studied in the full $\pt$ range accessible, up to 2 GeV/$c$. The cross section ratios $\sigma_\rho/\sigma_\omega$ and $\sigma_\phi/\sigma_\omega$ have been considered in full $\pt$ as a function of the size of the production target. The nuclear dependence of the production cross sections of the $\eta$, $\omega$ and $\phi$ mesons has finally been studied in terms of the power law $\sigma_\mathrm{pA} \propto \mathrm{A}^\alpha$, where the $\alpha$ parameter has been found to increase as a function of $\pt$.